The complete or partial detachment of ligaments, tendons or other soft tissues from their associated bones within the body are relatively commonplace injuries, particularly among athletes. Such injuries are generally the result of excess stress being placed on these tissues. Tissue detachment may occur as the result of an accident such as a fall, overexertion during a work related activity, during the course of an athletic event or in any one of many other situations and/or activities.
In the case of a partial detachment, commonly referred to under the general term "sprain", the injury will frequently heal itself, if given sufficient time, and if care is taken not to expose the injury to any undue stress during the healing process. If, however, the ligament or tendon is completely detached from its associated bone or bones, or if it is severed as part of a traumatic injury, partial or permanent disability may result. Fortunately, a number of surgical techniques exist for reattaching such detached tissues and/or completely replacing severely damaged tissues.
One such technique involves the reattachment of the detached tissue using "traditional" attachment devices such as metal staples, sutures over buttons and cancellous bone screws. Such "traditional" attachment devices have also been used to attach tendon or ligament substitutes (often formed of autogenous tissue harvested from elsewhere in the body) to the desired bone or bones.
Another technique is described in detail in U.S. Pat. No. 4,950,270 entitled "Cannulated Self-Tapping Bone Screw", issued to Bowman et al. on Aug. 21, 1990, which patent is specifically incorporated herein by reference. In this technique, the anterior cruciate ligament in a human knee, for example, is replaced and/or repaired by forming bone tunnels through the tibia and/or femur at the points of normal attachment of the anterior cruciate ligament. A ligament graft with a bone block on at least one of its ends is sized to fit within the bone tunnels. Suture is then attached to the outer end of each bone plug and thereafter passed through the femoral and/or tibial bone tunnels. The femoral plug and/or the tibial plug is (are) then inserted into the appropriate bone tunnel behind the suture. Subsequently, the suture is drawn tight (simultaneously in opposite directions, in cases where bone plugs are to be located in both a femoral bone tunnel and a tibial bone tunnel). This procedure positions the bone plug (or plugs) in the desired position, and imparts the desired degree of tension to the ligament or ligament substitute. Finally, a bone screw is inserted between each bone plug and the wall of its associated bone tunnel so as to securely lock the bone plug in position by a tight interference fit.
Alternatives to the foregoing use of bone screws are also well known in the art. For example, in U.S. Pat. No. 5,147,362 entitled "Endosteal Ligament Fixation Device" issued Sep. 15, 1992 to E. Marlowe Goble, rearwardly extending flexible barbs or pins are attached to the bone plug (either directly or by a collar, cap or similar intervening element) for anchoring a bone plug within a bone tunnel. The disclosure of the foregoing U.S. Pat. No. 5,147,362 is also incorporated herein by reference.
Similarly, in U.S. Pat. No. 4,997,433 entitled "Endosteal Fixation Stud and System" issued Mar. 5, 1991 to E. Marlowe Goble et al., a device is disclosed for attachment to the outer end of the bone plug. The device includes a pair of spaced, forwardly projecting, flexible arms. One of these arms includes a substantially rigid, radially and rearwardly projecting portion disposed adjacent its outer end. This device is adapted for insertion through a bone tunnel ahead of the bone plug such that the projection may engage the outer surface of the bone adjacent the far end of the bone tunnel. This projection acts to maintain the position of the bone plug within the bone tunnel so long as rearwardly directed tension is maintained on the repair material. The disclosure of U.S. Pat. No. 4,997,433 is also incorporated herein by reference.
It will be understood that repair methods of the types described above have not been uniformly successful. For example, rigid attachment using "traditional" attachment devices such as staples, sutures and screws often cannot be maintained even under normal tensile loads.
Also, the use of sharp screws to create a locking interference fit between a bone plug and a bone tunnel introduces problems. For one thing, there is always the possibility of damaging the ligament or repair material during insertion of the screw. In addition, it can be difficult to maintain the desired tension on the ligament or repair material during insertion of the screw. Also, the insertion of the screw requires that a twisting motion be imparted to the screw; this twisting motion can in turn cause rotation of the bone plug in the bone tunnel, and may lead to undesirable twisting of the ligament which is attached to the bone plug.
The removal of such bone screws can also cause problems. In those cases in which the screw can be removed simply by unscrewing it in the usual manner, an undesirable hole is left in the bone. In many cases, however, the screw cannot be simply unscrewed from the bone to remove it. In these situations, the screw must typically be either forceably pulled out of the bone or it must be removed by chipping away the surrounding bone. Both of these procedures can cause serious damage to the bone.
The foregoing attachment devices of U.S. Pat. Nos. 5,147,362 and 4,997,433 are also not totally satisfactory. This is because in the device of U.S. Pat. No. 5,147,362, the cross-sectional size of the bone tunnel must significantly exceed the cross-sectional size of the bone plug on account of the constructions utilized. This results in the bone plug being separated from the sidewall of the bone tunnel by a substantial gap, thereby slowing the assimilation of the plug into the bone during healing. The device of U.S. Pat. No. 4,997,433, on the other hand, is limited to use in a particular method of reattachment. Further, undesirable binding between the stud and the sidewall of the bone tunnel may occur as the stud's projection is forced through the bone tunnel.
Various types of suture anchors and anchors for attaching objects to bone are also well known in the art. A number of these devices are described in detail in U.S. Pat. Nos. 4,898,156; 4,899,743; and 4,968,315 (each of which being presently owned by Mitek Surgical Products, Inc., of Norwood, Mass., the assignee of this application). The disclosures of these patents are also incorporated herein by reference.